1. Technical Field
The present disclosure relates generally to a power supply apparatus, and more particularly to a redundant power supply apparatus.
2. Description of Related Art
Referring to FIG. 6, the related art in a field of redundant input power supply units typically connects multiple independent input power sources AC1, AC2 through a switching device 51 which selects one input power source as a primary input power source and other input power sources as secondary and tertiary, etc. input power sources for proper operation such that the input power source is received and converted by a power supply unit 52 to supply power to a power load of a server system, which is simply represented by a load 50. If the primary power source fails to meet certain criteria, the switching device 51 will disconnect from the primary power source, and the input power source that best meets the requirements for proper operation is selected. The requirements may be based on measured AC voltage or DC voltage, AC frequency, presence, or some other tracking means that allow instantaneous or near instantaneous determination of the ability to supply power as required by the system.
The switching device 51 can be electromechanical relays, semiconductor switches, or a combination of these devices. These systems typically require the input voltage to “break before make”, i.e. be disconnected before connected for safety reasons as one requirement would be that the two or more power sources be fully independent of each other or a fault would occur. In other words, the two input power sources AC1, AC2 can never be directly or indirectly connected together through an electrical path, such as an ohmic path. If an uncontrolled current flows, a few dangerous situations will arise to the safety system engaging elements such as circuit breakers or fuses.
Also, it would be possible to put a live AC voltage on a connector that is not intended to have a live AC voltage such as the prongs of an AC line cord. International agencies also require certain design requirements to electrical devices that connect to public utilities that provide user safety and acceptance. The switching device 51 must also be able to transition from one input to another fast enough so the operation of the power converted is not disrupted, thereby providing a redundant system that works as a continuously functioning power supply. The switching device 51 that typically performs this function is often called an automatic voltage switch (AVS) or automatic transfer switch (ATS) or other terms that describe the same function.
U.S. Pat. No. 5,939,799 discloses an uninterruptible power supply with a transfer switch. Referring to FIG. 7, the transfer switch 63 is connected between two power sources, i.e., a first power source 61 and a second power source 62, and an AC/DC converter 64. The transfer switch 63 is controlled by a switch control 65 for selectively receiving the first power source 61 or the second power source 62 of said AC power.
U.S. Publication 2014/0077602 discloses a power supply system and a method for controlling the same. Referring to FIG. 8 and FIG. 9, a circuit switching module 73 is connected between two power sources, i.e., a first power source 71 and a second power source 72, and a controllable AC/DC conversion module 74. The circuit switching module 73 is controlled by a control module 75 such that the circuit switching module 73 is switched to the first power source 71 or the second power source 72.
U.S. Publication 2015/0123473 discloses an uninterruptable power supply for device having power supply modules with internal automatic transfer switches. Referring to FIG. 10, the automatic transfer switches (ATSs) 83 are connected to two AC power sources, i.e., a first AC power source 81 and a second AC power source 82, and further connected to a power factor correction 84 and a DC/DC converter 85. The ATSs 83 are controlled by a micro-controller unit (MCU) 86 to determine whether the first AC power source 81 or the second AC power source 82 is delivered to the power factor correction 84 and the DC/DC converter 85.
U.S. Pat. No. 6,630,753 discloses a low cost redundant AC to DC power supply. Referring to FIG. 11, two power sources, i.e., a first power source 91 and a second power source 92, are connected together after bridge rectifiers 93, 94 with a line selected and determined by silicon controller rectifiers (SCRs) 95, 96. A galvanic isolation between the two power sources 91, 92 is absent such that the system could only be used in a low cost controlled situation such that it needs to make a big effort to verify the safety of the system given the possibility of devices failing short circuit.
However, the foregoing transfer switch, switching module, and circuit switching module are often unreliable because of their mechanical construction and are subject to contact welding, limited operating temperature range, and mechanical failures much more than electrical components.